In a chromatograph mass spectrometer, three-dimensional data consisting of the three axes of time, mass-to-charge ratio and signal intensity (e.g. output voltage) are collected by temporally separating the components in a sample with the chromatograph and acquiring a mass spectrum with the mass spectrometer by sequentially analyzing each component eluted from the chromatograph (for example, see Patent Literature 1). In a data processing system for a chromatograph mass spectrometer, a peak which appears on such three-dimensional data is detected, and the substance corresponding to that peak is identified from the peak position (retention time and mass-to-charge ratio) with reference to a previously-set identification table. Additionally, a mass chromatogram (i.e. a graph with the horizontal axis representing time and the vertical axis representing the signal intensity at a specific mass-to-charge ratio) related to a mass-to-charge ratio specific to a target component to be quantitatively analyzed is created from the three-dimensional data, and the height or area of the peak located at the retention time of the target component on the mass chromatogram is measured. Then, the concentration or quantity of the target compound is calculated with reference to a calibration curve showing the relationship between the peak-area value and the concentration (content) of the target compound which has been previously created based on the result of a measurement of a standard sample or similar substance.
In general, such a data processing system has limits on the magnitude of the signal that can be processed, due to hardware limitations of the signal-processing circuits including an A/D converter. The system cannot correctly perform calculations if the magnitude of the input signal is higher than the upper limit or lower than the lower limit.
Besides such a limitation related to signal processing, ion detection by a mass spectrometer involves the problem that the reliability of the detection result varies with the level of the signal. For example, if the concentration of the component in the sample is too low, the accuracy of the quantitative determination deteriorates due to the influence of the noise in the detection signal. Conversely, if the component concentration is too high, the non-linearity of the detection signal becomes noticeable, so that the accuracy of the quantitative determination similarly deteriorates. Accordingly, for an analysis using a conventional chromatograph mass spectrometer, the sample needs to be appropriately diluted so that the component concentrations in the sample will be included in a predetermined range (dynamic range).